Objectives: The long-term objectives of the proposed research project are: 1. To advance knowledge of methods and techniques for in-vitro cultivation of the erythrocytic stages of human and simian malarial parasities (Plasmodium falciparum and P. knowlesi respectively). 2. To advance knowledge of the metabolism and nutritional requirements of human and simian malarial parasites (P. falciparum and P. knowlesi respectively). To achieve the above objectives, the following specific areas of experimental investigations have been proposed: 1. To improve culture medium and technique for in-vitro cultivation of P. falciparum. 2. To study nutritional requirements for in-vitro growth of P. falciparum in a plasma-free culture medium. 3. To continue studies on nutritional requirements for in-vitro growth of P. knowlesi in a plasma-free culture system. 4. To study incorporation of labeled purines and pyrimidines into DNA and RNA of P. falciparum with special reference to the incorporation of thymidine into DNA.